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<?xml version="1.0" encoding="gb2312"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=gb2312"/><title>linux for ppc chapter 14               jacobw </title></head><body><center><h1>BBS 水木清华站∶精华区</h1></center><a name="top"></a>发信人:&nbsp;plato&nbsp;(纯真年代),&nbsp;信区:&nbsp;Embedded&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<br />标&nbsp;&nbsp;题:&nbsp;linux&nbsp;for&nbsp;ppc&nbsp;chapter&nbsp;14&nbsp;<br />发信站:&nbsp;BBS&nbsp;水木清华站&nbsp;(Wed&nbsp;May&nbsp;30&nbsp;23:20:24&nbsp;2001)&nbsp;<br />&nbsp;<br />Next&nbsp;Previous&nbsp;Contents&nbsp;<br />----------------------------------------------------------------------------&nbsp;<br />----&nbsp;<br />14.&nbsp;Floating&nbsp;Point&nbsp;<br />Some&nbsp;of&nbsp;the&nbsp;embedded&nbsp;PowerPC&nbsp;processors&nbsp;do&nbsp;not&nbsp;have&nbsp;a&nbsp;floating&nbsp;point&nbsp;unit,&nbsp;a&nbsp;<br />nd&nbsp;so&nbsp;must&nbsp;perform&nbsp;all&nbsp;floating&nbsp;point&nbsp;operations&nbsp;in&nbsp;software.&nbsp;Others&nbsp;do&nbsp;have&nbsp;<br />&nbsp;a&nbsp;hardware&nbsp;floating&nbsp;point&nbsp;unit,&nbsp;and&nbsp;may&nbsp;perform&nbsp;operations&nbsp;in&nbsp;hardware.&nbsp;<br />14.1&nbsp;Software&nbsp;<br />If&nbsp;your&nbsp;application&nbsp;has&nbsp;very&nbsp;intensive&nbsp;floating&nbsp;point&nbsp;requirements,&nbsp;you&nbsp;may&nbsp;&nbsp;<br />need&nbsp;to&nbsp;switch&nbsp;to&nbsp;fixed&nbsp;point&nbsp;or&nbsp;choose&nbsp;a&nbsp;target&nbsp;processor&nbsp;which&nbsp;does&nbsp;have&nbsp;a&nbsp;<br />n&nbsp;FPU.&nbsp;<br />Floating&nbsp;point&nbsp;can&nbsp;be&nbsp;performed&nbsp;either&nbsp;by&nbsp;instruction&nbsp;emulation&nbsp;in&nbsp;the&nbsp;kerne&nbsp;<br />l,&nbsp;or&nbsp;by&nbsp;compiling&nbsp;everything&nbsp;with&nbsp;-msoft-float.&nbsp;In&nbsp;particular,&nbsp;it's&nbsp;importa&nbsp;<br />nt&nbsp;that&nbsp;all&nbsp;the&nbsp;libraries,&nbsp;whether&nbsp;dynamically&nbsp;or&nbsp;statically&nbsp;linked&nbsp;are&nbsp;comp&nbsp;<br />iled&nbsp;with&nbsp;the&nbsp;same&nbsp;options&nbsp;as&nbsp;the&nbsp;binaries&nbsp;that&nbsp;use&nbsp;them.&nbsp;Unless&nbsp;you're&nbsp;usin&nbsp;<br />g&nbsp;a&nbsp;toolkit&nbsp;where&nbsp;this&nbsp;has&nbsp;already&nbsp;been&nbsp;done&nbsp;for&nbsp;you,&nbsp;this&nbsp;will&nbsp;generally&nbsp;me&nbsp;<br />an&nbsp;that&nbsp;if&nbsp;you&nbsp;wish&nbsp;to&nbsp;use&nbsp;-msoft-float&nbsp;to&nbsp;gain&nbsp;maximum&nbsp;performance,&nbsp;you&nbsp;nee&nbsp;<br />d&nbsp;to&nbsp;(re)compile&nbsp;everything,&nbsp;including:&nbsp;<br />All&nbsp;static&nbsp;and&nbsp;shared&nbsp;libraries&nbsp;<br />The&nbsp;compiler's&nbsp;internal&nbsp;libraries,&nbsp;such&nbsp;as&nbsp;libgcc.a&nbsp;<br />All&nbsp;executables&nbsp;<br />You&nbsp;will&nbsp;almost&nbsp;certainly&nbsp;not&nbsp;get&nbsp;this&nbsp;right&nbsp;first&nbsp;time.&nbsp;The&nbsp;primary&nbsp;symptom&nbsp;<br />&nbsp;is&nbsp;that&nbsp;printf&nbsp;gives&nbsp;bogus&nbsp;numbers&nbsp;for&nbsp;simple&nbsp;floating&nbsp;point&nbsp;values.&nbsp;<br />However,&nbsp;if&nbsp;you&nbsp;succeed,&nbsp;you&nbsp;can&nbsp;save&nbsp;space&nbsp;by&nbsp;configuring&nbsp;the&nbsp;kernel&nbsp;withou&nbsp;<br />t&nbsp;floating&nbsp;point&nbsp;emulation.&nbsp;<br />See:&nbsp;<a href="http://lists.linuxppc.org/listarcs/linuxppc-embedded/199911/msg00056.ht">http://lists.linuxppc.org/listarcs/linuxppc-embedded/199911/msg00056.ht</a>&nbsp;<br />ml&nbsp;<br />To&nbsp;add&nbsp;kernel&nbsp;math&nbsp;emulation&nbsp;to&nbsp;the&nbsp;2.2.13&nbsp;kernel,&nbsp;see:&nbsp;<a href="http://lists.linuxpp">http://lists.linuxpp</a>&nbsp;<br />c.org/listarcs/linuxppc-embedded/199912/msg00017.html&nbsp;<br />The&nbsp;&quot;paranoia&quot;&nbsp;test&nbsp;should&nbsp;give&nbsp;no&nbsp;complaints&nbsp;if&nbsp;everything&nbsp;is&nbsp;working&nbsp;corre&nbsp;<br />ctly.&nbsp;See:&nbsp;<a href="http://www.enseeiht.fr/NetLib/paranoia/index.html">http://www.enseeiht.fr/NetLib/paranoia/index.html</a>&nbsp;<br />14.2&nbsp;Hardware&nbsp;<br />If&nbsp;your&nbsp;CPU&nbsp;has&nbsp;an&nbsp;FPU,&nbsp;you'll&nbsp;want&nbsp;to&nbsp;use&nbsp;it.&nbsp;Make&nbsp;sure&nbsp;that&nbsp;everything&nbsp;is&nbsp;&nbsp;<br />consistently&nbsp;compiled&nbsp;for&nbsp;hardware&nbsp;floating&nbsp;point,&nbsp;especially&nbsp;if&nbsp;you've&nbsp;asse&nbsp;<br />mbled&nbsp;your&nbsp;toolkit&nbsp;yourself,&nbsp;or&nbsp;are&nbsp;using&nbsp;an&nbsp;8xx&nbsp;toolkit&nbsp;to&nbsp;compile&nbsp;for&nbsp;the&nbsp;&nbsp;<br />8260.&nbsp;<br />Programs&nbsp;compiled&nbsp;for&nbsp;hardware&nbsp;floating&nbsp;point&nbsp;can&nbsp;still&nbsp;run&nbsp;on&nbsp;a&nbsp;CPU&nbsp;without&nbsp;<br />&nbsp;an&nbsp;FPU,&nbsp;provided&nbsp;the&nbsp;kernel&nbsp;is&nbsp;built&nbsp;with&nbsp;the&nbsp;floating&nbsp;point&nbsp;instruction&nbsp;em&nbsp;<br />ulator.&nbsp;This&nbsp;incurs&nbsp;a&nbsp;further&nbsp;performance&nbsp;penalty&nbsp;on&nbsp;CPUs&nbsp;lacking&nbsp;an&nbsp;FPU.&nbsp;<br />14.3&nbsp;Mixed&nbsp;<br />If&nbsp;you&nbsp;are&nbsp;using&nbsp;a&nbsp;single&nbsp;set&nbsp;of&nbsp;shared&nbsp;libraries,&nbsp;you&nbsp;cannot&nbsp;mix&nbsp;the&nbsp;two&nbsp;te&nbsp;<br />chniques&nbsp;in&nbsp;the&nbsp;one&nbsp;system.&nbsp;If&nbsp;you&nbsp;link&nbsp;statically&nbsp;or&nbsp;try&nbsp;really&nbsp;hard&nbsp;by&nbsp;cre&nbsp;<br />ating&nbsp;two&nbsp;sets&nbsp;of&nbsp;shared&nbsp;libraries,&nbsp;the&nbsp;two&nbsp;can&nbsp;co-exist&nbsp;since&nbsp;programs&nbsp;comp&nbsp;<br />iled&nbsp;with&nbsp;-msoft-float&nbsp;never&nbsp;generate&nbsp;floating&nbsp;point&nbsp;instructions&nbsp;requiring&nbsp;&nbsp;<br />kernel&nbsp;emulation.&nbsp;<br />In&nbsp;general,&nbsp;you're&nbsp;better&nbsp;off&nbsp;choosing&nbsp;one&nbsp;or&nbsp;the&nbsp;other;&nbsp;and&nbsp;choosing&nbsp;hardwa&nbsp;<br />re&nbsp;floating&nbsp;point&nbsp;with&nbsp;kernel&nbsp;instruction&nbsp;emulation&nbsp;is&nbsp;much&nbsp;easier&nbsp;to&nbsp;get&nbsp;wo&nbsp;<br />rking&nbsp;correctly.&nbsp;<br />----------------------------------------------------------------------------&nbsp;<br />----&nbsp;<br />Next&nbsp;Previous&nbsp;Contents&nbsp;&nbsp;<br />&nbsp;<br />--&nbsp;<br />&nbsp;<br />※&nbsp;来源:·BBS&nbsp;水木清华站&nbsp;smth.org·[FROM:&nbsp;166.111.161.8]&nbsp;<br /><a href="00000014.htm">上一篇</a><a href="javascript:history.go(-1)">返回上一页</a><a href="index.htm">回到目录</a><a href="#top">回到页首</a><a href="00000016.htm">下一篇</a></h1></center><center><h1>BBS 水木清华站∶精华区</h1></center></body></html>
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